Reciprocating mechanism and engine including the same

ABSTRACT

A reciprocating mechanism for use in an engine comprises a reciprocating member which is movable in a substantially linear reciprocating direction between two ends of travel, a piston provided on the reciprocating member, and a constant breadth cam and follower, the follower being coupled directly to the reciprocating member to translate linear movement of the reciprocating member into rotary motion of the cam, and the mechanism being such that movement of the reciprocating member at the two ends of its travel is reversed in dependence upon the rotation of the cam, the follower lying below and to the side of the piston bore and the piston being rigidly mounted to the reciprocating member.

The benefit of the priority dates of the previously filed InternationalApplication designating the United States of America, PCT/GB99/02027having an international filing date of Jun. 28, 1999 and claimingpriority based on GB Application Serial No. 9813710.2, filed Jun. 26,1998 and GB Application 9900247.9, filed Jan. 8, 1999, are herebyclaimed.

FIELD OF THE INVENTION

The present invention relates to a reciprocating mechanism, and moreparticularly to an engine, such as an internal combustion engine,including such a mechanism.

DESCRIPTION OF THE PRIOR ART

Known reciprocating mechanisms include crank mechanisms and cammechanisms. Internal combustion engines exclusively use crank mechanismsto translate their linear motion of a piston sliding up and down in abarrel into rotation of an output shaft.

BRIEF SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided areciprocating mechanism including a reciprocating member, movable in asubstantially linear reciprocating direction between two ends of travel,a piston provided on the reciprocating member, and a constant breadthcam and follower, the follower being coupled directly to thereciprocating member to translate linear movement of the reciprocatingmember into rotary motion of the cam, and the mechanism being such thatmovement of the reciprocating member at the two ends of its travel isreversed in dependence upon the rotation of the said cam, wherein thefollower lies below and to the side of the piston bore and the piston isrigidly mounted to the reciprocating member.

Preferably, the constant breadth cam and follower member are coupled toa pendulum counterbalance.

According to a second aspect of the present invention, there is providedan engine including the reciprocating mechanism of the first aspect ofthe invention.

A piston may be provided at each end of the reciprocating member.

Reference will now be made, by way of example, to the accompanyingdrawings, in which:

FIG. 1 shows a front end view, partially sectioned, of apparatusembodying the first and second aspects of the present invention;

FIG. 2 shows a plan view of FIG. 1;

FIG. 3 is a schematic diagram showing a rear end view of the gearmechanism and the return mechanism shown in FIGS. 1 and 2;

FIG. 4 shows an alternative embodiment of the return mechanism of FIG.3;

FIG. 5 shows a perspective view of details of the return mechanism ofFIG. 4;

FIG. 6 shows a perspective view of the crank mechanism employed in theapparatus of FIGS. 1, 2 and 3;

FIG. 7 shows a perspective view of a reciprocating member embodying agear rack of 11, 12 shown in FIGS. 1 and 2;

FIG. 8 shows a plan view of a constant breadth cam member, coupleddirectly to the reciprocating member;

FIG. 9 shows a plan view of a lightened constant breadth cam and itssurface bearings;

FIG. 10 shows a bearing which supports the 15 surface bearings of thecam to the follower member;

FIG. 11 shows a perspective view of the follower member with analternative arrangement for bearing guides;

FIG. 12 shows a pendulum counterbalance;

FIG. 13 shows an exploded perspective view of the reciprocating memberand the constant breadth cam member; and

FIGS. 14A and 14B show respective perspective front and rear views ofthe combined reciprocating member and constant breadth cam member.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1, 2 and 3 show a reciprocating mechanism embodying the firstaspect of the present invention employed in an internal combustionengine and including a reciprocating member 1, connected to two pistons2, one at each end, rotary means 3 and reversing means 4.

The reciprocating member 1 is a shaft embodying a rack of gears 11,12provided partially along its length on opposing longitudinal sides.Regions 13 which do not have any gear teeth are provided at each set ofgear teeth. The reciprocating member 1 also includes means 15, such as atransverse hole or axle, for attaching the gear rack 11,12, and also forattaching a connecting rod of an adjacently disposed crank mechanismthereto. Bearing blocks 16 are provided on both sides of gears 11,12 tomount reciprocating member 1 slidably in a fixed linear path formovement between two ends of travel. The reciprocating member 1 ispreferably made from a light alloy material and the rack 11,12 from ahigh strength material, the member 1 being made as light as possible.The pistons 2 are preferably connected rigidly to the reciprocatingmember 1, one at each end, and this may be by way of a screw thread orpin and clip.

The rotary means 3 comprises two gear wheels 31 which are coupled toeach other to rotate in the same direction at substantially the samerate, that is at substantially the same angular velocity. These gearsmay be sprag clutch, ramp and roller type gears, which rotate in onedirection and free wheel in the opposite direction, or they may besegmented gears as shown. Each segmented gear wheel 31 has a gearedportion 32 and a non-geared portion 33. The geared portions 32 arearranged engageably to couple the gear teeth 11,12 of the reciprocatingmember 1, whilst the non-geared portions 33 are arranged not to engagewith these gear teeth 11,12 at any time. Each gear wheel may have abearing 161. As shown in FIG. 4, on the same axis of each gear wheel 31,behind or in front of each portion 32,33, gears 34 are provided whichengage with each other via an intermediate gear disposed therebetween.

The geared and non-geared portions 32,33 of each gear wheel 31 areadapted to enable one gear wheel 31 to engage the reciprocating member 1in one of its two directions of travel and to enable the other gearwheel 31 to engage the reciprocating member 1 in the opposite direction,whilst both gear wheels rotate together in the same sense.

Therefore, whilst one gear wheel 31 is arranged to engage its teeth 32with teeth 11, for example, of the reciprocating member 1, the otherwheel 31 rotates without engagement, with the non-geared portions 33passing over the teeth 12. At the two ends of travel of thereciprocating member, the gear wheels 31 are both disengaged from teeth11,12. This disengagement is necessary if the gear wheels 31 are to beable to rotate at constant angular velocity, whilst reciprocating member1 almost instantaneously stops and reverses at each of its ends oftravel. The sprag clutch and ramp and roller gears 31 may stay inengagement with gear teeth 11,12, as they will rotate in one directionof travel and free wheel around their axis on the return oppositedirection of travel.

An intermediate gear wheel 35 provides an output for the mechanism andthis may lead to a gear box (not shown). It may also be desirable totake the drive output from either of gear wheels 31, gear wheel 35acting as an idler coupling gear wheel. Desirably, the intermediate gearwheel 35 and the gear wheels 31 rotate with substantially constantangular velocity. This may require the reciprocating member 1 to movewith constant speed between substantially both ends of its travel,whilst changing very quickly its direction of travel and its speed ateach end. To give the reciprocating member 1 more time to stop andaccelerate at a lesser rate in the opposite direction at each end oftravel to match the speed of the rotating gear wheels 31, the gearwheels 31 may both be out of engagement with teeth 11,12 for a shortdistance of travel of the reciprocating member 1 at each end. To allowthe reciprocating member 1 to have a non-constant speed, whilst giving aconstant angular velocity output at gear wheel 35, the gear wheel 31 mayhave varying radii which co-operate with teeth 11, 12 which areconfigured accordingly. A larger radius, with constant gear wheelangular velocity, will allow the reciprocating member 1, arrangedtangentially to the gear wheel, to travel faster. This is preferablynear the middle of each stroke. Conversely, a smaller radius will allowthe reciprocating member 1 to travel slower. This is preferably near theends of its travel. The gear wheels employed in all cases, may ofcourse, be helical gears which have high contact ratios.

Reversing means 4 are shown in FIGS. 1 to 3 as one arrangement or inFIGS. 1, 4 and 5 as an alternative arrangement. In each case, thereversing means 4 includes two connecting rods 41, a central crank 44with two crank arms, and a reciprocating mechanism 38 or 39 which iscoupled to the central crank 44. Referring additionally to FIGS. 6 and7, the connecting rods 41 are rotatably mounted at one of their ends 42to the reciprocating member 1 at the said two locations 15 thereon androtatably mounted to the crank 44 at their other ends 43. The crank armsare preferably arranged when the reciprocating member 1 is at either endof its travel as shown in FIG. 1, such that a respective connecting rod41 extends between the centre of the crank axis and the locations 15 onthe reciprocating member 1. In this way, the crank 44 and connectingrods 41 prevent the piston 2 and reciprocating member 1 from movingfurther than beyond the desired ends of travel and colliding with thecylinder head 21(only one shown) for each piston. The reversing means 4is operable to stop and reverse the reciprocating member 1 at each ofits ends, of travel. This is achieved by rotating the crank 44 from theposition shown in FIG. 1, clockwise, to draw the reciprocating member 1to the left so that the distance between the connecting rod and crankaxis is made to reduce, at the same time as the reciprocating member 1reaches its limit of travel.

FIG. 3 shows a mechanism 38 which causes the crank 44 to turn when thereciprocating member 1 nears the ends of its travel. The mechanism 38comprises a displacement cam 45 (constant breadth cam shown), rack andfollower member 46, which is coupled to the crank 44 via a rack andpinion joint 44 and 46. The surface of the cam 45 which is driven bycoupled gear wheel 31 acts to displace the rack and constant breadthfollower member 46, the displacement motion rotating crank pinion 44into the desired synchronous rotation of the crank at each of the endsof travel of reciprocating member 1. A roller bearing may be provided atthe contact point between the surface of the cam 45 and the rack andfollower member 46.

FIGS. 4 and 5 show an alternative reciprocating mechanism 39. Themechanism 39 includes a further crank mechanism which couples the gearwheel 31 to the crank 44. As the gear wheel 31 rotates, reciprocatingmotion is imparted to a connecting rod member 47 which is provided withgear teeth 50. The thus generated reciprocal motion is synchronous withthe desired rotation of the crank at each of the ends of travel ofreciprocating member 1. The connecting rod member 47 is coupled to thecrank via a rack and pinion joint 44,47.

An internal combustion engine employing one of the above reciprocatingmechanisms may function with two or four stroke engine technology.Referring to FIG. 1 as a starting position, a two stroke embodiment ofan engine functions as follows:

(I) both gear wheels 31 are rotating clockwise, combustion and explosionof fuel-air mixture causes the piston 2 and the reciprocating member 1to accelerate to the left, aided by the clockwise rotation of the crank44 and anti-clockwise rotation of the right-hand-side connecting rod 41from top dead-centre position, both sets of gears 31,11,12 aredisengaged from each other;

(II) the lower gear wheel 31 rotates with its non-geared portion movingunder the leftwardly-moving teeth 12 of the reciprocating member 1, theupper gear wheel 31 now engages the teeth 11 of the reciprocating member1, as it matches the tangential speed of its geared portion 32, thecrank mechanism 41, 44 moves freely to allow the reciprocating member 1to displace and ensures the teeth 11 mesh with gear teeth 32 of theupper gear wheel 31;

(III) the right-hand side piston is driven to the left, down its barrel,as the fuel-air mixture burns and escapes via an exhaust outlet, as theupper gear wheel is driven by teeth 11, the mixture in the left-handside barrel starts to become compressed;

(IV) the left-hand-side mixture is further compressed and its respectiveconnecting rod 41 and crank 44 approaches a top-dead-centreconfiguration, the geared portion 32 of the upper gear wheel 31 losesits engagement with teeth 11 and the non-geared portion 33 of the lowergear wheel 31 nears its engagement with teeth 12, ignition of thecompressed mixture takes place; and

(V) the crank mechanism 41, 44 reaches top-dead-centre and thereciprocating member 1 is brought to rest, both gear wheels 31 aredisengaged from the teeth 11,12, the crank 44 is started to be rotatedanti-clockwise to return reciprocating member 1, ignition of mixturedevelops into combustion and explosion.

FIGS. 8 to 14 show an alternative reciprocating mechanism 40, whichunlike that of FIG. 1 includes no gears. The reciprocating mechanism 40includes a reciprocating member 1, wherein the geared section of themechanism shown in FIG. 1 is replaced by shoulders 58 (refer to FIGS. 8and 13) which connect and couple against parts 57 of a constant breadthfollower member 51 (refer to FIGS. 8, 11, 13 and 14) Alternatively (notshown), the reciprocating member 1 may be formed as an integral unitwith the constant breadth follower member 51. The linear motion of thereciprocating member 1 is thereby transferred to the constant breadthfollower member 51, in which surface bearings 53, supported by furtherbearings 54 (FIG. 10), are housed. The surface bearings 53 bear againsta constant breadth cam 52 which is accordingly rotated by the displacedsurface bearings 53, thereby rotating a drive output shaft 59 (not shownin all views) connected to the cam 52. The profile of the cam 52 may bechanged to effect a desired change in the speed of the reciprocatingmember 1/piston 2. The constant breadth follower member 51 may beprovided with bearing guides 55 (FIG. 13) which can slide in a bearingmount (not shown). Alternatively, circular bearings 56 may be attachedwhich slide on shafts (FIG. 11).

Desirably, to achieve balance, at least four reciprocating mechanisms 40are provided (not shown) in an engine, the cams 52 of the two mechanismsin the centre of the arrangement rotating in the same direction, andthose on either side of the centre rotating in the opposite direction.

Alternatively, as shown in FIG. 12, a counterbalance pendulum 60 may beconnected to the constant breadth follower 51, the pendulum 60comprising a rod, connected at one of its ends to a surface bearing 53of the follower member 51, a pivot 62 provided at the other end of therod, a pivot 61 provided between the two ends of the rod, a shaft 63connected to the pivot 62, and a mass 64 slidably mounted on the shaft63. As the mass from 53 moves to the right, so the rod pivots aroundpivot 61 and pivot 62 moves to the left, thereby causing mass 64 to movealong the shaft 63, thus creating a counterbalance (bearings and guidesnot shown).

An internal combustion engine employing such a reciprocating mechanism40 may function with two or four stroke engine technology. Referring toFIG. 8 as a starting position, a two stroke embodiment of an enginefunctions as follows:

(I) combustion and explosion of fuel-air mixture causes the right-handpiston 2 and hence the reciprocating member 1 and follower member 51 toaccelerate to the left;

(II)the right-hand surface bearing 53 moves with the follower member 51,thereby bearing against the cam 52 and rotating the cam 52 in ananti-clockwise direction;

(III) the right-hand side piston is driven to the left, down its barrel,as the fuel-air mixture burns and escapes via an exhaust outlet, themixture in the left-hand side barrel starts to become compressed;

(IV) the left-hand-side mixture is further compressed, as the camcontinues to rotate, ignition of the compressed mixture takes place; and

(V) ignition of mixture develops into combustion and explosion, theleft-hand piston 2 accelerates to the right and hence the linear motionof the reciprocating member 1 and follower member 51 is reversed,thereby causing the left-hand surface bearing 53 to bear against the cam52 and cause it to continue rotating in an anti-clockwise direction.

From the foregoing, it will be observed that numerous variations andmodifications may be effected without departing from the spirit andscope of the invention. It is to be understood that no limitation withrespect to the specific apparatus illustrated herein is intended orshould be inferred. It is, of course, intended to cover by the appendedclaims all such modifications as fall within the scope of the claims.

What is claimed is:
 1. A reciprocating mechanism for an enginecomprising a reciprocating member, movable in a substantially linearreciprocating direction between two ends of travel, a piston provided onthe reciprocating member, and a constant breadth cam and follower, thefollower being coupled directly to the reciprocating member to translatelinear movement of the reciprocating member into rotary motion of thecam, and the mechanism being such that movement of the reciprocatingmember at the two ends of its travel is reversed in dependence upon therotation of the cam, wherein the follower lies below and to the side ofthe piston bore and the piston is rigidly mounted to the reciprocatingmember.
 2. A mechanism as claimed in claim 1, wherein the constantbreadth cam and follower are coupled to a pendulum counterbalance.
 3. Anengine including a reciprocating mechanism comprising a reciprocatingmember, movable in a substantially linear reciprocating directionbetween two ends of travel, a piston provided on the reciprocatingmember, and a constant breadth cam and follower, the follower beingcoupled directly to the reciprocating member to translate linearmovement of the reciprocating member into rotary motion of the cam, andthe mechanism being such that movement of the reciprocating member atthe two ends of its travel is reversed in dependence upon the rotationof the cam, wherein the follower lies below and to the side of thepiston bore and the piston is rigidly mounted to the reciprocatingmember.
 4. An engine as claimed in claim 3, wherein a piston is providedat each end of the reciprocating member.
 5. An engine as claimed inclaim 3, wherein the constant breadth cam and follower are coupled to apendulum counterbalance.
 6. An engine as claimed in claim 4, wherein theconstant breadth cam and follower are coupled to a pendulumcounterbalance.